The Sun Ring Battle is the first match of the Vongola Ring Conflict. It is the battle between the candidates for the title of Tenth Generation Vongola Sun Guardian, Ryohei Sasagawa and Lussuria. The match took place in the recently constructed Sun Arena in Namimori Middle School.
In order to gain the Vongola Sun Ring and the right to be the next generation's Sun Guardian, Ryohei and Lussuria participate in the first round of the Ring Battle.
The Cervello instruct Ryohei and Lussuria to enter the Sun Arena, a special arena prepared specially for the Sun Guardians' Match. Before Ryohei enters the ring, Takeshi Yamamoto suggests they form a group circle. Ryohei, thinking it is a good idea, forces Tsunayoshi Sawada and Hayato Gokudera to huddle together with him and Yamamoto, and cheers for himself. Ryohei and Lussuria enter the ring and after checking that their rings are real, Cervello announces the rules.
Ryohei takes off his clothes, earning a compliment from Lussuria saying that he's his type and that he is taking him home. Ryohei ignores him enters his Boxing stance. Lussuria, mocks him while also entering his Muay Thai stance. The Cervello signals the start of the battle and illuminates the surrounding area with blinding light. Unable to see his opponent, Ryohei is attacked by Lussuria who is wearing a pair of sunglasses. Ryohei tries to attack the air, hoping to get lucky and land a punch on Lussuria. However, Lussuria uses this as an opening and attacks from the side, causing Ryohei to be thrown to the edge of the ring and burned by the ropes.
As Ryohei stands up, he luckily lands a hit on Lussuria. However, Belphegor reveals that Lussuria is merely playing with Ryohei and got hit on purpose. Knowing that his opponent is in midair, Ryohei attacks with a jab, unknowingly punching Lussuria's Metal Knee. As Ryohei suffers from his injuries and dehydration from the blinding lights, Colonnello, his trainer, arrives and orders him to show Lussuria his true strength.
While Lussuria belittles the power of his punches, Ryohei stands up and reveals that he has been using his only left hand to attack. As Ryohei explains the power of his right hand, Lussuria does a fast footwork, leaving multiple afterimages of himself. Ryohei concentrates on where the real Lussuria is and uses a Maximum Cannon. However, Lussuria belittles him again and reveals that Ryohei didn't really hit him. But Ryohei reveals that his target was not really Lussuria but the lights which were destroyed, enabling Ryohei to open his eyes. Lussuria is impressed and initially afraid that Ryohei is able to destroy the lights with his fist but Belphegor points out that Ryohei's body is covered with salt produced from evaporating sweat which he placed on his fist and used as pellets.
Lussuria gains confidence and used the salt on Ryohei's body to destroy more lights. As Lussuria uses his footwork, Ryohei uses his Maximum Cannon again. However, he accidentally hits Lussuria's metal knee and injures himself. Just then, Kyoko Sasagawa arrives together with Hana Kurokawa and Tsuna's dad, Iemitsu Sawada. After seeing Ryohei covered with wounds, Kyoko tries to stop him from fighting but Ryohei promises that he won't lose and gets up. Ryohei uses another Maximum Cannon which is able to break Lussuria's metal knee and defeat him.
Ryohei demands Lussuria to give up the ring, but he refuses and wishes to continue the fight. Lussuria is then attacked from behind by his comrades for being weak, prompting the Cervello to announce that he is unable to move. After Cervello announces the next match and the Varia leaves, Ryohei hands Tsuna the two halves of the sun ring and leaves with his sister.